1. Technical Field
The present invention relates to an automatic leveling device and an automatic leveling method for correcting an optical axis direction of a headlight of a vehicle.
2. Related Art
A vehicle height of a vehicle body is changed in a front-back direction by boarding of a passenger or loading and unloading, and sometimes the optical axis of the headlight is orientated upward compared with an initial state. A driver of an oncoming vehicle is easily dazzled when the optical axis of the headlight is orientated upward. Therefore, there is well known an automatic leveling device that detects an inclination of the vehicle to automatically correct the optical axis direction of the headlight (for example, see Japanese Patent No. 3782634).
In the automatic leveling device, an actuator is driven to adjust the optical axis direction of the headlight based on information concerning a vehicle height difference from front and rear height sensors. The actuator includes a motor that adjusts the inclination of a headlight reflector and a motor driver that drives the motor.
FIG. 8 is a conceptual view for explaining an operation example of an actuator in an automatic leveling device in the related art. In FIG. 8, a horizontal axis indicates elapsed time and a vertical axis indicates a voltage value fed into the actuator. That is, FIG. 8 illustrates the state in which the voltage value is relatively changed as time advances. One-to-one correlation holds between the voltage value fed into the actuator and the headlight reflector inclination adjustment that is of an output of the actuator. The actuator has a hysteresis characteristic in order to prevent frequent optical axis correction in consideration of a lifetime of the motor. A shaded portion of FIG. 8 indicates a hysteresis range. The motor is started up when an instruction position signal from a control ECU is set out of a hysteresis range, and the motor is stopped when the instruction position signal is matched with an actuator position signal indicating an actual position of the actuator.
In FIG. 8, because the instruction position signal once runs out of the hysteresis range, the movement of the actuator position signal is started from that point, and the movement is continued until the instruction position signal and the actuator position signal overlap each other. This is an example in which the intended correction can be performed. The hysteresis range is set in a constant range according to an occasional position of the actuator position signal. Accordingly, the hysteresis range is changed when the actuator position is moved.
FIGS. 9 and 10 are conceptual views for explaining another operation example of the actuator in the automatic leveling device in the related art. Thanks to the hysteresis characteristic, the motor movement caused by an unnecessary fluctuation of the instruction position signal is eliminated. At the same time, as illustrated in FIG. 9, when the instruction position signal does not run out of the hysteresis range, the actuator is not driven, and sometimes the intended correction cannot be performed. In order to avoid the event, there is well known a control method. As illustrated in FIG. 10, after the actuator is driven by once setting the instruction position signal out of the hysteresis range, the instruction position signal is set to the target value to be actually set again, and the actuator is driven to the originally intended position.